Rooftop solar, once installed is often assumed to crank power without any attempt to test its efficiency as time elapses. Apart from the collection of debris on panels or some other obvious obstacle to proper operation. Other things to cause problems are a shadow cast from a new, neighboring construction.
There are tests that are readily performed and that provide clues as to what’s going on with the installation. Both panel failure and inverter failure or the occurrence of frequent high line voltage causing the inverter to switch off AC power production. The latter is a real issue that now affects the bulk of solar. Insiders in the electricity distribution business know about the troubles they go through trying to adjust on line tap changers—and somehow never getting it right. It has contractors reading up on inverter manuals to alter the settings so that power can still be pushed out at 254 volts, single phase.
What can cause damage to solar panels?
Leaves, dead birds and other small animal life caught between panels and the roof that can cause excessive local heating or cause excessive leakage current to earth. These can be eliminated before trouble starts. What is not realized is that panels do degrade over time—and that can be checked with a suitable insulation tester. The insulation test is between the negative and positive rails with respect to earth.
Thin panels are more subject to potential induced degradation than thick panels. The voltage across the cells with respect to the grounded frame causes a drift of sodium ions in the protective glass to damage the performance of cells. Atmospheric contaminants, such as chlorides (in marine environments) and sulfur dioxide and nitrous oxides (in industrial locations), are deposited on array structures. Once deposited, the contaminants react with oxygen and water and typically increase corrosion rates by releasing electrons from the metal’s surface. It is interesting to note that corrosion rates can be effectively decreased in areas of high rainfall, as contaminants are regularly washed away from the structural materials.
How should Insulation Testing be done?
The way the insulation testing is normally done is by shorting the positive and negative rails and doing one insulation measurement to earth. It is smart to first isolate the panels with the DC isolation switch. However, a better way to test the panels is to measure both the positive and negative rails separately.
The Hioki IR4053 https://www.hioki.com/file/cmw/hdTechnicalDataEn/50/attached_file/?action=browser&log=1&lang=en is designed for solar panel testing; it will measure open circuit voltage, and can measure both rails for insulation strength to earth without having to short the positive and negative terminals. Another test to gauge panel performance is a short circuit test which will indicate problems such as photocell failure. The Hioki CM4376 )with Bluetooth that will allow you to easily get into tight spaces with their new innovative slimline jaw) will measure DC panel current as well operating voltage and can also be used on the inverter output to measure AC current and therefore power. https://www.hioki.com/en/products/detail/?product_key=6476-
Even Solar panels with good guarantees can break down.
Solar panels of good quality come with meaningful guaranties of performance and can be expected to perform efficiently over decades, but even so untimely failure of panels is always a distinct possibility. No matter the care taken during installation, microcracks in the glass surface of panels possibly caused during transport or during placement, can in due course, cause panel failure or at least, reduce panel efficiency sufficiently that reduction in power output is more than a few percentage points.
Some examples of the types of problems we are talking about
Bypass diode failures can cause Hot Spots
Hotspots in panels can develop through faults in manufacture, through opens in bypass diodes or some other reason but with the same effect, the avalanche breakdown of a cell (the photovoltaic cell is a current generator and a diode in parallel—normally not conducting, and reverse biased if the cell is shaded). In practice, testing bypass diodes is a bit of a pain. They are frequently encapsulated, therefore precluding tests but if accessible, then testing is possible, for example in ground installations.
Can you test Opens and Shorts on bypass diodes?
Yes you can. There are special purpose bypass diode testers that allow open and short tests in broad daylight . Yes no more night time testing! The Hioki FT4310 https://www.hioki.com/en/products/detail/?product_key=6415 is a special field test instrument for testing opens and shorts on bypass diodes. Panels can continue to operate more or less satisfactorily in terms of string current but if finally, an open occurs, the whole string is knocked out therefore causing a notable decline in inverter power output.
Although not frequently used for domestic installations, the I-V (current and voltage curve) tracer is ideal for testing panel performance as well as string tests. https://emona.com.au/products/electronic-compliance-testing/solar-pv-testing/solarlink-kit.html An actinometer measures the intensity of the sunlight, and a ‘sweeping panel load’ traces out the current-voltage curve of the panel. In some instruments this can be compared to standard panels by reference to panel model/type stored curves.
Testing instrumentation can be limited by using AC/DC clamp meters that have sufficient range to measure open circuit voltages and that have Hall-effect clamps suitable for DC current measurement. They therefore are well suited to measuring the operation of inverters as both DC power and AC power can be measured.
Improper operation of your Solar system is going to cost you more than just lost revenue off your power bills.
You can safely bet on the market for solar systems continuing to increase in demand and also that proper operation of domestic systems will be more and more important. Why? Because in due course—it’s already mooted by the Australian Energy Market Commission (AEMC) that domestic connections to the grid will have to pay a fee for the ‘privilege’ of being able to pump out power—and this is irrespective of whether solar systems are working properly or not.